1. Field of the Invention
The present invention relates to a screw refrigerating apparatus using a screw compressor.
Conventionally, a screw refrigerating apparatus using a screw compressor is publicly known (see Patent Document 1, for example).
2. Description of the Related Art
The screw compressor is roughly categorized into an oil-cooled type screw compressor and an oil-free type screw compressor. In an oil-cooled type screw compressor, oil is filled in a rotor room in order to seal between rotors, and between the rotors and an inner wall surface of the rotor room, to cool parts whose temperature increases due to compressing, to lubricate, and the like. In an oil-free type screw compressor, oil is not filled into a rotor room, bearings are completely sealed from the rotor room with a seal, and a synchronous gear is used for transmitting a rotation drive force between male and female rotors. In terms of the structure of a main unit of the compressor, the oil-free type screw compressor is considerably complex compared with the oil-cooled type screw compressor, and the oil-free type screw compressor is more expensive than the oil-cooled type screw compressor by the increased complexity while it is assumed that the same quantity of air is discharged. Further, compared with the oil-cooled type screw compressor, the oil-free type screw compressor has larger gaps between the rotors, and between the rotors and the inner wall surface, and a larger quantity of gas leaks through these gaps. Therefore, the oil-cooled type screw compressor is generally used, and the oil-free type screw compressor is not used except for a special case where compressed gas is not allowed to contain lubricant, and only clean compressed gas is required.
In a screw refrigerating apparatus described in Japanese Unexamined Patent Application Publication H1-273894, an oil-cooled type screw compressor is used, the refrigerant gas sucked by the screw compressor is discharged from the screw compressor along with oil after compressed while being filled with the oil in the rotor room. Thus, an oil separating and collecting unit (oil separator) for separating and collecting the oil from the compressed refrigerant gas discharged from the screw compressor, an oil cooling unit (oil cooler) for cooling the collected oil, an oil filter (oil strainer) for cleaning the oil, and an oil flow passage for leading the oil into the rotor room again after passing through these units, and passage for repeating circulation of the oil are provided.
The conventional screw refrigerating apparatus described above has following problems: The oil separating and collecting unit, the oil cooling unit, the oil filter, and an oil piping for the oil flow passage are required. These units occupy a large portion with respect to the volume of the overall apparatus. The apparatus becomes bulky. The installation space increases. The apparatus has more complicated structure. The cost increases accordingly, simultaneously, maintenance exerts a heavy burden, and the like.
The present invention was devised for eliminating these conventional problems as its objective, and is intended to provide a screw refrigerating apparatus for simplifying the structure, reducing the size, reducing the burden of the maintenance, and the like.
To solve the problems described above, in a first invention, in a screw refrigerating apparatus comprising a refrigerant circulating passage which includes a screw compressor, a rotor room within said screw compressor, a condenser, an expansion valve, and an evaporator, the screw refrigerating apparatus comprises throttle means and a bypass flow passage branching at a part of the refrigerant circulating passage between the condenser and the expansion valve, routing through the throttle means, and communicating with the rotor room.
Since the bypass flow passage is provided in this way, and the cooled refrigerant in the mixed gas/fluid state is led to the rotor room of the screw compressor, and provides the effects of lubricating, sealing, and further cooling in the rotor room, even when a screw compressor has the same structure as a screw compressor which is conventionally designed as oil-cooled type is employed for the screw refrigerating apparatus according to the first invention, it is no longer necessary to fill lubricant into the rotor room for the effect of the lubricating, sealing, and cooling, and it is possible to eliminate apparatuses, piping and the like for the lubricant which leads only the lubricant into the rotor room and circulates the lubricant. Namely, while if lubricant is used for above mentioned lubricating, sealing and cooling, an oil separating and collecting unit, an oil cooling unit, an oil filter, an oil flow passage for circulating lubricant including these apparatuses for lubricant, and the like are necessary, the constitution described above according to the first invention entirely eliminates these apparatuses for lubricant and the piping, and the like, and provides effects of enabling simplifying the structure, reducing the size, reducing the burden of the maintenance, and the like.
A second invention has such a constitution that refrigerant circulating in the refrigerant circulating flow passage contains a quantity of lubricant as much as restraining a decrease of heat transfer efficiency due to the lubricant in the condenser and the evaporator to a practically negligible degree, in addition to the constitution according to the first invention.
Consequently, the second invention provides effects of enabling lubricating the bearings, preventing the parts from corroding where the lubricant circulates, and increasing the durability of them in addition to the effects of the first invention.
A third invention has such a constitution that the bypass flow passage branches from a top part of the refrigerant circulating flow passage when the specific gravity of the lubricant is lower than the specific gravity of the refrigerant, and the bypass flow passage branches from a bottom part of the refrigerant circulating flow passage when the specific gravity of the lubricant is higher than the specific gravity of the refrigerant, in addition to the constitution according to the second invention.
Consequently, an effect of enabling further increasing the effects of the second invention is provided.
A fourth invention has such a constitution that comprising a discharged refrigerant temperature detector provided for detecting the refrigerant temperature between the screw compressor and the condenser, and for outputting a temperature signal indicating the detected temperature, and a variable throttle valve employed as the throttle means interposed on the bypass flow passage, wherein the variable throttle valve increases its opening as the detected temperature becomes high, in addition to the constitution according to any one of the inventions 1 to 3.
Consequently, even when a load on the refrigeration changes, the quantity of the refrigerant led from the bypass flow passage II to the rotor room is always maintained properly such that the discharge temperature of the screw compressor 11 is maintained to a desired value.
A fifth invention has such a constitution that comprises a driving unit of the screw compressor comprising an inverter and a variable speed motor controlled by the inverter, a temperature detector for detecting the refrigerant temperature inside the evaporator, and for outputting a temperature signal indicating the detected temperature, and a controller for receiving the temperature signal, and for outputting a control signal to the inverter to change the rotation speed of the variable speed motor so that the detected temperature is equal to a set temperature, in addition to the constitution according to any one of the inventions 1 to 4.
A sixth invention has such a constitution that comprises a driving unit of the screw compressor comprising an inverter and a variable speed motor controlled by the inverter, a pressure detector for detecting the refrigerant pressure between the evaporator and the screw compressor, and for outputting a pressure signal indicating the detected pressure, and a controller for receiving the pressure signal, and for outputting a control signal to the inverter to change the rotation speed of the variable speed motor so that the detected pressure is equal to a set pressure, in addition to the constitution according to any one of the inventions 1 to 4.
Consequently, with the fifth and sixth inventions, even when the oil is not used, the capacity of the screw compressor can be adjusted by controlling the rotation speed of the variable speed motor with the inverter, thereby providing an effect of enabling maintaining the refrigerating capability properly, in addition to the effects of any one of the first to fourth inventions.
In a seventh invention, in a screw refrigerating apparatus comprising a refrigerant circulating passage which includes a screw compressor, a rotor room within the screw compressor, a condenser, an expansion valve; and an evaporator, the screw refrigerating apparatus comprises a fluid lubricated bearing inside the screw compressor, first throttle means, a bypass flow passage branching at a part of the refrigerant circulating passage between the condenser and the expansion valve, routing through the first throttle means, and communicating with the rotor room, second throttle means and a bearing-fluid-filling flow passage branching at a part of the refrigerant circulating passage between the condenser and the expansion valve, routing through the second throttle means, and communicating with the fluid lubricated bearing.
Therefore, it is not either necessary to provide a flow passage for supplying the bearings with oil, thereby further simplifying the constitution of the apparatus, and eliminating the labor of maintenance operation, in addition to the effects of the first invention.